The synthesis of various periphery-substituted shape-persistent cage compounds by twelve-fold condensation reactions of four triptycene triamines and six salicyldialdehydes is described, where the substituents systematically vary in bulkiness. The resulting cage compounds were studied as permanent porous material by nitrogen sorption measurements. When the material is amorphous, the steric demand of the cages exterior does not strongly influence the gas uptake, resulting in BET surface areas of approximately 700 m² g⁻¹ for all cage compounds 3 c–e, independently of the substituents bulkiness. In the crystalline state, materials of the same compounds show a strong interconnection between steric demand of the peripheral substituent and the resulting BET surface area. With increasing bulkiness, the overall BET surface area decreases, for example 1291 m² g⁻¹ (for cage compound 3 c with methyl substituents), 309 m² g⁻¹ (for cage compound 3 d with 2-(2-ethyl-pentyl) substituents) and 22 m² g⁻¹ (for cage compound 3 e with trityl substituents). Furthermore, we found that two different crystalline polymorphs of the cage compound 3 a (with tert-butyl substituents) differ also in nitrogen sorption, resulting in a BET surface area of 1377 m²g⁻¹, when synthesized from THF and 2071 m²g⁻¹, when recrystallized from DMSO.

In recent years, the development of porous materials derived from discrete organic molecules made a substantial progress towards high-surface-area materials with distinct properties. One major advantage in comparison to existing, well-established porous polymers is their solubility, making such compounds potential valuable precursors for “processing porosity”. One important parameter of porous compounds is their specific surface area. The possibilities to reach ultra-high-surface-area materials from this new type of porous compounds are critically discussed.

The synthesis of two novel tetrakis(salicylaldehydes) based on a rigid tetraphenylmethane core is presented. These salicylaldehydes were used as precursors for the construction of three-dimensional multimetallic salphens, as exemplified by the synthesis of rigid and shape-persistent tetranuclearzinc–, nickel– and palladium–salphens with defined geometries and distances between the metal sites. The UV/Vis measurements of the tetranuclear metal complexes are presented.

The cover picture shows tetrahedral shape-persistent tetranuclear metal–salphens (with Zn²⁺, Ni²⁺, and Pd²⁺ as metal ions) and their absorption spectra. The basis for the synthesis of the metal–salphens is the tetrakis(salicylaldehyde), depicted at the center. Details are discussed in the article by M. Mastalerz and I. M. Oppel on p. 5971 ff.

Ein Bereich der supramolekularen Chemie umfasst die Synthese diskreter dreidimensionaler Aggregate durch Koordination von Übergangsmetallen. Ein Teil dieses Gebiets ist die Chemie der supramolekularen Käfigverbindungen, die durch Knüpfung koordinativer Bindungen entstehen. Heute kennt man ein breites Spektrum solcher supramolekularen Koordinationskäfige. Relativ selten sind jedoch analoge organische Käfigverbindungen, die aus kovalenten Bindungsbildungen resultieren. In letzter Zeit wurden auf diesem Gebiet einige wichtige Fortschritte erzielt, nicht zuletzt durch Anwendung neuer Konzepte wie der dynamischen kovalenten Chemie. Diese Konzepte machen es möglich, organische Käfigverbindungen in wenigen Stufen und guten Ausbeuten zu synthetisieren, und das meist aus einfach zugänglichen Ausgangsverbindungen.

One area of supramolecular chemistry involves the synthesis of discrete three-dimensional molecules or supramolecular aggregates through the coordination of metals. This field also concerns the chemistry of supramolecular cage compounds constructed through the use of such coordination bonds. To date, there exists a broad variety of supramolecular cage compounds; however, analogous organic cage compounds formed with only covalent bonds are relatively rare. Recent progress in this field can be attributed to important advances, not least the application of dynamic covalent chemistry. This concept makes it possible to start from readily available precursors, and in general allows the synthesis of cage compounds in fewer steps and usually higher yields.